Preprocessor transformations for implementing greedy and service provider-level QoS-based adaptation for BPEL scenario execution

Kareliotis, Costas Vassilakis, Efstathios Rouvas, Panayiotis Georgiadis
SDBS Lab technical report, August 2012

In this technical report, we describe and exemplify the transformations applied by the WS-BPEL preprocessor, in order to produce a BPEL scenario that can be adapted according to QoS specifications, in the architecture described in [1]. [1] adopts a greedy algorithm for performing adaptation, i.e. it uses only the QoS specifications pertaining to the first invoke activity IA to a specific service provider S, so as to decide the service provider to which both IA and further invocations to operations provided by S will be directed. The greedy algorithm may result in suboptimal bindings, while in some cases it may even lead to situations where the middleware is unable to find any appropriate service selection for fully servicing the BPEL scenario, albeit such a path does exist. To this end, a service provider-level adaptation strategy can be employed: the transformed scenario may communicate to the ASOB middleware [1] the information concerning all operation invocations to a specific partner link before the first invocation an operation provided by the specific partner link is executed, and therefore the ASOB middleware can exploit this information to remedy the problems stemming from the greedy nature of the adaptation method specified in [1].